Question

我需要有关我的autofac泛型配置的帮助。我收到以下错误，但似乎无法解决。我有一个使用泛型的接口，称为IScript<TOptionType>。

实现该接口的是一个名为Script<TOptionType> : IScript<TOptionType>的抽象类。从该抽象类派生出两个具体的类，它们设置了它们首选的TOptionType。

我已经上传了一个示例.net核心应用程序，该应用程序在此处显示了问题：https://github.com/Strandedpirate/agr

要运行，请转到agr\autofac-generic-registration并输入dotnet run。

C＃似乎没有问题，将具体类型装入接口或抽象基类。那么为什么autofac在这里抱怨呢？

C:\Users\strandedpirate\source\repos\agr\autofac-generic-registration (master -> origin)
λ dotnet run

Unhandled Exception: System.ArgumentException: The type 'agr.TableScript' is not assignable to service 'agr.Script`1'.
   at Autofac.Builder.RegistrationBuilder.CreateRegistration(Guid id, RegistrationData data, IInstanceActivator activator, Service[] services, IComponentRegistration target) in C:\projects\autofac\src\Autofac\Builder\RegistrationBuilder.cs:line 192
   at Autofac.Builder.RegistrationBuilder.CreateRegistration[TLimit,TActivatorData,TSingleRegistrationStyle](IRegistrationBuilder`3 builder) in C:\projects\autofac\src\Autofac\Builder\RegistrationBuilder.cs:line 132
   at Autofac.Builder.RegistrationBuilder.RegisterSingleComponent[TLimit,TActivatorData,TSingleRegistrationStyle](IComponentRegistry cr, IRegistrationBuilder`3 builder) in C:\projects\autofac\src\Autofac\Builder\RegistrationBuilder.cs:line 249
   at Autofac.ContainerBuilder.Build(IComponentRegistry componentRegistry, Boolean excludeDefaultModules) in C:\projects\autofac\src\Autofac\ContainerBuilder.cs:line 240
   at Autofac.ContainerBuilder.Build(ContainerBuildOptions options) in C:\projects\autofac\src\Autofac\ContainerBuilder.cs:line 148
   at agr.Program.Main(String[] args) in C:\Users\strandedpirate\source\repos\agr\autofac-generic-registration\Program.cs:line 22

Program.cs

class Program
    {
        static void Main(string[] args)
        {
            var builder = new ContainerBuilder();

            // comment out the next registrations to see the program run.
            builder.RegisterType<TableScript>()
              .As<Script<TableScriptOptions>>()
              .InstancePerLifetimeScope();
            builder.RegisterType<TableScript>()
              .As(typeof(Script<>))
              .InstancePerLifetimeScope();
            builder.RegisterType<TableScript>()
              .As(typeof(IScript<>))
              .InstancePerLifetimeScope();

            // explodes here during autofac building.
            var container = builder.Build();

            // if you comment out the above autofac configuration this will succeed compile and run-time.
            // why does c# have no problems converting TableScript to IScript<T> and Script<T> but autofac is complaining?
            TestInterface(new TableScript());
            TestAbstractBase(new TableScript());

            using (var scope = container.BeginLifetimeScope())
            {
                Console.WriteLine("Resolving IScript instance...");
                var instance = scope.Resolve(typeof(IScript<>)) as IScript<object>;
                instance.Run();
            }
        }

        static void TestInterface<T>(IScript<T> a)
            where T : class, new()
        {
            Console.WriteLine($"{nameof(TestInterface)} called - {a.CanHandle("table")}");
        }

        static void TestAbstractBase<T>(Script<T> a)
            where T : class, new()
        {
            Console.WriteLine($"{nameof(TestAbstractBase)} called - {a.CanHandle("table")}");
        }
    }

IScript.cs

public interface IScript<TOptionType>
        where TOptionType : class, new()
    {
        bool CanHandle(string key);
        Task Run();
        bool Validate(TOptionType options);
    }

Script.cs

public abstract class Script<TOptionType> : IScript<TOptionType>
        where TOptionType : class, new()
    {
        public abstract bool CanHandle(string key);

        public abstract Task Run();

        public virtual bool Validate(TOptionType options)
        {
            return true;
        }
    }

TableScript.cs


    public class TableScript : Script<TableScriptOptions>
    {
        public override bool CanHandle(string key)
        {
            return key == "table";
        }

        public override Task Run()
        {
            Console.WriteLine($"{nameof(TableScript)} executed");
            return Task.CompletedTask;
        }
    }

FileScript.cs

    public class FileScript : Script<FileScriptOptions>
    {
        public override bool CanHandle(string key)
        {
            return key == "file";
        }

        public override Task Run()
        {
            Console.WriteLine($"{nameof(FileScript)} executed");
            return Task.CompletedTask;
        }
    }

Answer 1

有两个问题。

首先，您的TableScript注册：

builder.RegisterType<TableScript>()
       .As(typeof(Script<>))
       .InstancePerLifetimeScope();
builder.RegisterType<TableScript>()
       .As(typeof(IScript<>))
       .InstancePerLifetimeScope();

您正在尝试将封闭的通用注册为开放通用。如果您考虑这意味着什么，那就像在说“ TableScript可以为T和Script<T>允许任何IScript<T> 。”例如，我看到了TableScript : Script<TableScriptOptions>-开放的通用注册正在说的是它应该以某种方式也适用于Script<IntegerScriptOptions>或可能在尖括号内的其他任何内容。

相反，将其注册为封闭的通用名称。而且，我建议您在同一注册中执行此操作，否则根据有效的服务，您可以在整个生存期内获得两个TableScript的不同实例。

builder.RegisterType<TableScript>()
       .As<Script<TableScriptOptions>>()
       .As<IScript<TableScriptOptions>>()
       .InstancePerLifetimeScope();

接下来，IScript<T>的分辨率：

scope.Resolve(typeof(IScript<>)) as IScript<object>;

认为Resolve与new很像。如果您不能使用new或Activator.CreateInstance（基本上）来代替它，那么它将无法使用。例如，您不能执行以下操作：

// This isn't a thing
new Script<>();

您也不能像这样将开放的泛型放入对象的构造函数中：

public class MyClass
{
  // This also isn't a thing
  public MyClass(IScript<> script) { /* ... */ }
}

您无法更新开放的通用名称。编译器需要知道T中的Script<T>。同样，您无法解析开放的泛型。那没有道理。您必须解决一个封闭的泛型。

scope.Resolve<IScript<TableScriptOptions>>();

如果您真的想使用反射，则仍然必须使其成为封闭的泛型。

var script = typeof(IScript<>);
var options = typeof(TableScriptOptions);
var closed = script.MakeGenericType(new Type[] { options });
scope.Resolve(closed);

XXX类型无法分配给服务YYY

1 个答案: